


Under-swap!

by Reader_San



Category: Undertale (Video Game)
Genre: Crack, F/F, F/M, I Don't Even Know, Parody, This Is STUPID
Language: English
Status: Completed
Published: 2018-01-28
Updated: 2018-01-28
Packaged: 2019-03-10 13:37:22
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,510
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13502615
Author URL: https://archiveofourown.org/users/Reader_San/pseuds/Reader_San
Summary: You have an obligatory sleepover at Undyne's with the skelebros and Alphys, but after getting blackout drunk, everyone's swapped bodies!Oh noes!((Seriously though, I'm just making a little fun of Sans X Reader fanfics. Just a tiny bit. Even though I read all of them since I have no shame and no life.))(((Don't read if you're easily offended))))





	Under-swap!

You didn't know how, but when you woke up from being blackout drunk, the first thing you saw was yourself.  
Which was weird because there was no mirror in the living room.  
So you went closer to inspect yourself.  
Except, your body wasn't moving with you.  
"what the fuck?" You cursed and touched the mirror.  
Except it was no mirror, but literally your body.  
Your eyes widened when you saw a skeletal hand touching your body instead of the human one you were used to.  
"what the actual fuck?!" You stood up and looked at your??? skeletal hands.  
"Sans?" Your body asked.  
"no??? i'm reader? what are you talking about???" You clarified, confused as hell.  
Though, the voice that came from you wasn't yours but Sans' low barritone voice.  
"No, you're Sans." Your body said slowly.  
"i have no idea what happened but who the hell are you and what are you doing in my body?" You asked.  
"Your body? What are you talking about? This is clearly minnnnnnnee....." Your body trailed off as they looked down.  
"WHAT?! WHAT HAPPENED?! WHY AM I IN READER'S BODY?!" Your body shrieked, suddenly standing up and looking at it.  
Undyne stirred awake and looked between the two of you in confusion.  
"Woah... Am I still dreaming? Why is there a second version of me?" Undyne asked sleepily. Oh! That must be Sans!  
"sansy boi! you're undyne now! suplex a boulder!" You said excitedly.  
"No? I'm not Undyne. I'm Sans." Undyne said, narrowing her? His? Only eye.  
"then how come you can only see out of one eye? " You asked, crossing your arms.  
Undyne's eye out up in realization and looked down at her??? His??? Body in haste.  
"Well fuck." Undyne chuckled.  
"Stop cursing!" You??? Papyrus??? Scolded.  
"Sorry bro." Undyne apologized. You and you??? Papyrus looked at each other in amazement.  
"woah! you can spot your brother that easily? man, that's so cool." You complimented.  
"Stop looking so starstruck. It looks weird on me." You frowned and furrowed your bonebrows instead.  
"That's even worse." You chuckled and shook Papyrus' body awake.  
"Huh? Sans? What's happening?" Papyrus??? Said sleepily.  
"who are you?" You asked. Papyrus' bonebrows furrowed up in confusion.  
"Alphys, what do you mean?" Alphys asked.  
"hey pap, i found alphys in your body!" Poor Alphys looked so lost.  
"Hello Alphys! It seems we've all been bodyswapped! So now you are in my body!" Papyrus clarified.

"How does that even work?" Alphys asked.  
You pointed at her??? His??? Body.  
Her eyesockets bulged out comically at the sight of it.  
"WHAT?! I'M PAPYRUS NOW??? HOW???" You snorted at her freakout and calmed her down.  
"we have no idea." You admitted and woke Alphys' body up.  
"hello? wake up sleepyhead!" You yelled into her earhole???  
Alphys woke up with a start and shrieked.  
"you okay undyne?" You asked with a shiteating grin.  
"I'M GOING TO FUCKING DUST YOU SANS!!!" Alphys shrieked angrily and tried to summon a spear. Keyword tried.  
"The hell?" She looked at her empty hand and her eyes widened.  
"What. The. Fuck? Why am I Alphys?" She asked you.  
"i dunno. why am i sans?" You asked back.  
"So what you are trying to say is that you're not Sans?" You nodded.  
"Then which one of you punks is Sans?" She asked grumpily.  
You all pointed at Undyne's body.  
"Of course. Of fucking course. The universe must fucking love me." Alphys muttered bitterly to herself.  
"You better not have done anything to my body, capiche?" She threatened.  
"i mean, he's been awfully fishy about it if you ask me." You said, shrugging and giving her that slow wink that you find so infuriating.  
".... Who the hell are you?" She asked all of a sudden.  
"pretty sure i'm reader." You said.  
"Good." She said and slapped you.  
"ouch! what the hell? i only have one hp, so show some mercy!" You hissed, holding your cheekbone.  
"Well, I asked because I would never hurt my Alphys or Papyrus. And now that I think about it, neither would make terrible puns like the comedian over there." She said and pointed a thumb at her body.  
"i'm just trying to live up to my role." You mumbled.  
"This isn't some fucking roleplay or a fucking fanfiction, this is real life! And we are stuck in each other's bodies!" She huffed angrily.  
"hey, alphys. how do you feel about your body being so agressive to the weakest monster in the entire underground?" She sputtered for a while and Sans??? Came up to you and carried you away from the fuming Undyne??? Alphys???  
"Stay here you little troublemaker." He??? She??? Said and patted your head??? Skull???  
You huffed and blew him a raspberry.  
"holy shit, i have a magical blue tongue!" You exclaimed and looked at it with wonder.  
"look sans!" You said and stuck out your tongue.  
"I know. It's my body." He muttered. You blinked and retreated it.  
"you're such a sourpuss." You grumbled and crossed your arms.  
"Errr, Reader? Why is there a weird feeling underneath my stomach area?" Papyrus??? You??? Asked.  
"perhaps you need to go to the toilet." You suggested.  
"Ah yes! The toilet! I have no idea how!" Papyrus admitted proudly???  
"let's go. i ain't gonna have you peeing yourself." You said, standing up.  
"Wait, wait, wait. You're going to the toilet with him?" Sans??? Undyne???? Asked.  
"well, do you have any better solution? besides, it's my body so it really doesn't matter." You said and went to the bathroom together with Papyrus???  
You closed the bathroom door and Papyrus looked at you in expectation.  
"Now what?" He asked.  
You flipped open the toilet lid.  
"first, you have to take off your pants." Papyrus looked at you weirdly.  
"you don't have to look down." You added.  
He did as you said and asked you about the next step.  
"now you sit on the toilet seat." He did so.  
"now you pee." He blinked several times in confusion.  
"And how do you do that?" You sighed and tried to come up with a way to explain it to a skeleton with no genitals.  
"it's like channeling your magic out or something. can you feel that you are filled to the brim with something?" He nodded.  
"try to flow it out like it's a bunch of pent up magic that you need to release." It took a few tries, but he finally managed to pee.  
"LOOK READER! I DID IT! I PEED!" Papyrus exclaimed happily.  
"i'm so proud of you pap!" You stated, proud that you managed to teach a skeleton stuck in your body how to pee.  
You snorted at the irony.  
"Now what?" You explained that he needed to wipe himself dry and put on the pants.  
"What about the pee?" He asked curiously.  
"there's this handy button right here that flushes it down the drain." You explained and flushed.  
"And now?" He asked.  
"you wash your hands. pretty sure that you can do it without my help." You said and exited the bathroom.

"Where's Papyrus?" Sans asked.  
"Washing his hands." You answered, putting your hands into your pockets.  
"SANS! I KNOW HOW TO PEE!" Papyrus excitedly exclaimed once he left the toilet.  
Sans flushed in secondhand embarrassment.  
"I eh, am proud of you?" He said unsurely.  
Papyrus was absolutely beaming right now, which looked hella weird on you.  
"now that we got toilet issues aside, let's focus on the current problem." You said.  
"Yeah! Alphys, do you have an idea?" Undyne asked.  
"Well, I mean, no. I've never heard of people swapping bodies before. Unless it's from an anime." She said.  
"whelp, were doomed. there goes our only hope. might as well make yourselves comfortable, because we might never get back into our bodies." You said and sunk into the fluffy jacket.  
"not that it is that big of a problem since i get to have this jacket. it's a lose-win situation." You said and snuggled further into it. It's really comfy.  
You could just fall asleep.  
"HEY! Wake up! We can't just give up before we've even tried!" Undyne said and shook you awake.  
"huh, what? what's happening?" You asked half asleep and yawned.  
"You managed to fall right asleep in a whopping 5 minutes! I don't know whether to be impressed or disappointed." Papyrus explained.  
"cool." You said and stretched.  
"so did you figure something out?" You asked Alphys' body.  
"Well, no, but it can't be that hard to." Undyne admitted.  
"bummer. i guess i'll have to prepare pap for when my period comes and how to human." You said.  
"What's a period?" Sans put his scaly hand over your grin, glaring at you to shut up.  
"it's the full stop of a sentence." You explained.  
Sans retreated the hand, satisfied with your answer.  
"But I already knew that!" He said.  
Then Papyrus stared at you intensely and started blushing.  
"uuuhhh....?" You started dumbly, not knowing how to proceed.  
"Why do I have the sudden urge to call you cute and sexy?" You gave him a disturbed look and laughed uncomfortably.  
"damn pap, keep your dirty secrets to yourself! i mean, your brother is right there!" Papyrus shrieked in mortification and hid his flushed face behind his hands.  
"I didn't mean it like that!" You smirked.  
"riiiight. you keep telling yourself that. i'm sure sans will have a greeeat time explaining incest to you." Sans gave you a dirty glare and Undyne and Alphys felt veery uncomfortable being in this situation.  
"wait a second, let me try something... sans, what do feel when you look at undyne?" You asked.  
"I feel... Undying love towards her???" You snorted at Undyne's disturbed face.  
"and what do you feel undyne?" She stared at him intensely.  
".... Like he means the world to me. My saving grace." She explained cautiously.  
"and what do you feel Alphys towards me?" You asked.  
"Except for the overbearing brotherly love and every positive emotion there is towards you, not much." You awed and looked at Papyrus, who was flushing red.  
"do you feel that strongly towards sans? that's so cute." You said and slung an arm over him.  
A swell of emotions blossomed in your chest at the sudden contact and you could barely contain yourself.  
You pinned Papyrus to the floor, feeling your right eyesocket burning bright blue and you growled sexily at him.  
"you're so goddamn cute, i can barely contain myself sometimes. i just want to make you MINE." You growled darkly.  
Then you managed to snap out of it and backed up as much as you physically could against the foot of the couch.  
"uuuuuuh, what the fuck?" You asked and looked up at Sans, who was sweating nervously.  
"i think you have a problem, sans. incest is no good. get some professional help." You said, disturbed as all hell by what just happened. Papyrus was mirroring your expression to the T.  
"Reader, I don't think it was directed towards Papyrus." Undyne???? Alphys??? Said.  
"then who?" You asked, confused.  
Something clicked and you cautiously looked up at him, who was avoiding eyecontact.  
"do you feel that way about me?" You asked slowly.  
He started sweating even more at that.  
"jesus fucking christ, sans the skeleton is a yandere and i'm the victim." Sans and Papyrus looked at each other in confusion while Undyne and Alphys cackled madly at your outburst.  
"anime." Was all you said to explain it to them. It didn't help.  
"Awwwww, does little ol' Sansy have a crush on Reader?" Undyne teased.  
"Did you already forget who is in your body?" He said, crossing his arms.  
That shut her up.  
"pap, do you have my phone?" He checked the pockets and found it.  
"thanks." You typed in "how to deal with a crush" on Google.  
"What are you doing?" Sans asked.  
You showed him what you had been searching for.  
"in this wiki article, it doesn't say anything about letting your emotions blossom into something twisted. all it says is that you should confess before it's too late." You said.  
"Duly noted..." Sans grumbled.  
"now, we need to stop sidetracking! we need to get back into our bodies!" You said and googled "how to get back into your own body if it has been swapped".  
"oh, hey. google has the answer right here!" You said and continued reading.  
"Okay... And what do we do?" Sans asked.  
"basically it says that it's only temporary so we just have to wait it out." You said and pocketed your phone.  
"And how do we know if we should trust it?" Undyne asked.  
"i mean, what's the harm of it? if you want, we could look for another solution in the meantime." You suggested.  
~*~  
Hours later, you are still looking for an answer. Sans had fallen asleep not even twenty minutes into the search.  
"maybe we should take a break. we aren't anywhere closer than we did at the beginning." You suggested. Alphys and Papyrus nodded, but Undyne refused.  
"No! I don't want that lazy slob in my body any longer than I have to!" Undyne protested.  
"Gee, thanks Undyne." Sans said sarcastically.  
"where you just pretending to be asleep?" You asked.  
"Nah. But Undyne sure is loud." Undyne feigned offense to that.  
"What?! How dare you!" Luckily, Alphys was able to grab her before she might try to destroy her own body.  
"Calm down Undyne. You should use your anger to look for an answer instead of trying to dust your own body." Alphys suggested.  
Undyne grumbled but stayed put.  
Sans gave her a shiteating grin that challenged her.  
"sans..." You warned.  
He rolled his single eye but still wore that smile.  
"i don't know about you guys, but i'm beat. i'm going to take a break." You announced and sat on the sofa next to Sans.  
"It's probably because you had the unluck of being in Sans' lazy body!" Papyrus said.  
You chuckled and looked at Sans.  
He suddenly grew stiff and the smile he wore earlier is strained.  
"you ok?" You asked, raising an bonebrow in concern.  
"Uh, yeah. I hope so." He said.  
There was a silence between the two of you as neither of you knew how to proceed.  
"I'm sorry." Sans said, sighing.  
"why?"  
"Because I let my emotions grow into.... That." He said, not knowing how to explain it any further.  
"aww, don't worry! i forgive you!" You said.  
"Hey lovebirds! I'm going to dust the both of you if you're making out in my body!" Undyne roared.  
You laughed at the genuine concern laced in her voice.  
She actually thinks that you two would do that! Which sounded hella weird with Alphys' voice.  
"you don't have to worry undyne! because skeletons have no lips! isn't that right pap?" Papyrus gave you a thumbs up.  
You stretched and yawned.  
"welp, i'mma take a nap. you joining me?" You asked Sans.  
He shrugged, but ultimately shook his head, which surprised you.  
"Undyne's body doesn't need as much nap as me, making it physically impossible for me to recharge as there is no need for it." He explained.  
You nodded in understanding.  
"that makes sense. or should i say it makes sans?" You replied with a slow wink and hands behind your skull.  
Sans gave out a snicker, but immediately stopped when he heard how weird it sounded.  
"night." You said and went out like a light.  
~*~  
When you awoke, it was probably in the middle of the night as everyone was asleep.  
Well, everyone except you and Sans.  
"hey sans? what brings you here to this side of the 'you should be asleep' town?" You asked, noticing him pacing around mindlessly around the living room.  
"I'm Undyne, remember? I've already had my fill and any more sleep will make me agitated and restless." He tiredly responded and sat next to you.  
You hummed.  
"Ya know, when Pap said out loud his desires, that wasn't his, now was it?" He asked.  
You looked anywhere but him.  
"i, uh, hope so. it would be really awkward if it weren't the case. guess you're just seeing right through me." You said with another slow wink.  
He didn't take the bait and pressed on further.  
"So that means you have some sort of feelings towards me if you have the desire to call me sexy. Though, I have no idea what you see in this ol' bag of bones." He said, sounding more tired.  
"i'd make you think otherwise right now if it weren't for my promise to undyne." You said, smirking and lidding your eyesockets.  
As he processed the meaning of this, he flushed as red as his red ponytail. Well, his for the time being.  
"Aheh, that's dangerous stuff you're saying to this possessive freak. You shouldn't do that." He warned, sweating nervously.  
"fine. i'll let you off the hook. for now." You said and closed your eyesockets.  
You cracked open one and looked at him one final time.  
"but don't expect me to let you off that easily once i'm back into my own body~!" You said with a primal growl at the end and clamped shut your eyesocket and drifted off to sleep.  
Meanwhile, Sans was having an internal battle at your words.  
Holy mackerel, that was so hot coming from you, but an incredible turn off that it sounded exactly like himself.  
He'd heard himself thinking and saying similar things, but at the same time, it came from you! He knows it was you, but his instincts is just making him feel ego eccentric when he thinks like that.  
Oh well, you'd all go back to your old bodies and that would give him the perfect chance to properly confess. Because honestly, seeing himself flirting with him weirded him out.  
~*~  
When you all awoke, you felt extremely sore.  
Groaning, you stretched and stood up.  
You saw Sans napping on the end of the couch and you smirked mischievously.  
You took out a whoopie cushion from his pocket and lifted his head.  
Then you gently put it on the armrest and made him sit more upright.  
You then proceeded to hurry back to your spot and watch everything unfold with a grin.  
It was glorious.  
Sans' skull went down in his sleep, and just like you predicted, it hit the whoopie cushion, making a loud fart noise that startled everyone awake.  
Sans even fell to the floor in his panicked, half asleep state!  
You were laughing your ass off at the disapproving looks everyone gave you.  
But that laughter quickly turned into hoarse coughs.  
"Really Papyrus?" Undyne asked, looking completely done.  
"HEY, THAT WASN'T ME!" Papyrus protested.  
She slowly blinked and looked down at her body.  
"Hey, we're back in our own bodies!" She said, ecstatic to have the comedian out of her body.  
"I guess so." You said, smiling tiredly.  
You just noticed the strain on your vocal cords.  
"Goddammit Papyrus, my throat hurts!" You hissed. He apologized sheepishly.  
"Well, my girlfriend and I got work to do, so I guess I'll see you three later?" Undyne said, surpressing a smirk as she looked in between you and Sans.  
You narrowed your eyes, but said nothing.  
Undyne was elbowing Papyrus out of your peripheral vision and he quickly caught on.  
"OH! I, EH, NEED TO GO BUY GROCERIES NOW THAT I AM BACK IN MY OWN BODY! AND I NEED TO GET USED TO IT AGAIN!" He declared, standing up.  
You gave him a disbelieving look, not buying anything he said(heh), but bid farewell to the trio.  
Once they left, a silence hung over you and Sans.  
"so, uh... do you want to leave as well, or...?" Sans asked you. You shook your head no.

"Nah. Besides, I have some things to fulfill." You purred and slowly walked up to him.  
He raised a bonebrow in question, but flushed a brilliant blue in realization.  
You got close to him, just inches apart from his face, but stopped.  
"Hey, is it alright if I ki---" your sentence got cut off by Sans smashing his grin onto your lips. It was honestly a rather awkward kiss since he has no lips, but it's the intention that matters.  
A thought crossed you.  
How does one french kiss a skeleton...?  
You snorted and broke apart.  
He looked up at you in confusion.  
"How does one french kiss a skeleton?" You accidentally blurted out.  
He shrugged, looking just as confused about the matter as you.  
"Oh God, I'm gonna stay up late at night just trying to figure that out." You said, groaning.  
"... me too. and it's all your fault!" He blamed. You sheepishly grinned.  
"Sorry. Genuine question." You apologized.  
"Anyways, does that mean that we like each other or something? I mean, usually kissing after confession means dating.... Or...?" You asked, confused.  
"i guess? i mean, i like you a lot. and i would love to take you out on a date."He admitted.  
"Great! I like you too, so dating it is!" You declared, lips curling into a smile.  
".... Now what?"

**Author's Note:**

> Please don't get offended! And I didn't even put any effort into this lol  
> (((Oh God, why did I do this?)))  
> ((((And I might or might not be poking fun at fontcest shippers...))))


End file.
